As well as established methods such as computed tomography (CT) and magnetic resonance tomography (MRT), 3D imaging using a C-arm is also available for an imaging diagnosis of cerebral diseases such as a stroke, arteriovenous malfunction or AVM and cancers. All these methods have in common the fact that they supply morphological information relating to the tissue.
The flow of blood through tissue, in other words the perfusion of an organ for example, is a further important functional parameter. By determining a perfusion parameter (blood throughflow parameter) it is possible to identify, locate and determine the extent of a blood throughflow problem. It is possible to use such information, in particular by determining a number of perfusion parameters, to plan an optimum therapy and to check its success by a repeat determination.
Until now imaging methods such as computed tomography (CT) and magnetic resonance tomography (MRT) have been used to determine tissue perfusion. With such methods a contrast agent bolus is injected into a vein and the flow of the contrast agent into the tissue is tracked by imaging. Such a method, also known as bolus tracking, is described for example in the article by Leif Oestergaard, “Principles of cerebral perfusion imaging by bolus tracking”, Journal of Magnetic Resonance Imaging. 22(6): 710-717. Such methods however only supply information about the overall perfusion of the tissue, as the contrast agent used to record the image can only be injected into a peripheral vein.
Selective injection of the contrast agent into an artery is not possible while the patient is in an MRT or CT device. This is because the insertion of a catheter into an artery to administer the contrast agent is only possible with image-based guidance, as provided for example by an interventional x-ray device, e.g. an angiography device. The images produced by an MRT or CT device are not suitable for monitoring the insertion of a catheter into an artery. If in practice for example a selective arterial injection of the contrast agent is required, the patient to be treated must be transported between the catheter laboratory and the CT or MRT examination room. This considerable transportation outlay means that in practice only a few vessels can be included in the examination.
Embolization is an example of an important intervention-based method for treating bleeding, vessel malformations or tumors with a large number of blood vessels by occluding the blood vessels. Every effort is made only to close off the affected blood vessels where possible, without endangering the surrounding healthy vessels in the process. One example of a tumor with a large number of blood vessels is a meningioma (brain tumor) and the therapy of choice to treat such a tumor is an operation, in which the blood vessels leading to the tumor are increasingly frequently specifically occluded by means of interventions in preparation for the operation, to minimize blood loss during the operation. However such embolization requires a precise knowledge of the blood vessels supplying the tumor. As well as a simple angiograph it is also very helpful here to measure the perfusion and in particular the blood volume in 3D.
A specific problem that frequently occurs with meningiomas in particular is that such a tumor is supplied by way of various blood vessels. Embolization however has to be highly selective in order to ensure the supply to the brain parenchyma even after embolization. It is therefore essential to determine the supplying blood vessels and the areas of the tumor with blood flowing through carefully before the operation by means of a number of selective or superselective arterial contrast agent injections.
The embolization of meningiomas by means of perfusion imaging was described for example by A. J. Martin, S. Cha, R. T. Higashida, S. P. Cullen, V. Halbach, C. F. Dowd, M. W. McDermott and D. A. Saloner in “Assessment of Vasculature of Meningiomas and the Effects of Embolization with Intra-arterial MR Perfusion Imaging: A Feasibility Study”, AJNR Am. J. Neuroradiol., October 2007, 28: 1771-1777. Here Martin et al. describe a method for interventional angiography and catheter placement, combined with a perfusion measurement by means of magnetic resonance (MR). In this process an angiographic system is used to position a catheter by means of an intervention with simultaneous fluoroscopy in a vessel supplying the meningioma (e.g. in the external carotid artery (Arteria carotis externa)). The patient is then transferred to the MRT system and perfusion is measured with a selective contrast agent injection. Perfusion is then measured by means of selective contrast agent injection into a further vessel supplying the tumor. The not very selective carotid artery (Arteria carotis communis) is however selected here. The reason for this restriction is that the catheter can only be moved into this position by simple retraction, as the patient would otherwise have to be moved back into the fluoroscopy system and then be transferred back to MR once the catheter had been repositioned. Patient transportation makes this procedure very cumbersome and the evaluation and interpretation of the results is very complicated, as two true superselective contrast agent injections cannot be carried out.
Generally there is also a need or the necessity for other applications, such as the perfusion of liver tumors, the perfusion of the brain parenchyma after a stroke, etc., to obtain information about the resulting overall perfusion of defined structures based on a number of selective or superselective individual contrast agent injections.